(1) Field of the Invention
This invention relates to a process for preparing a sintered body comprising AlN and containing SiC, and more particularly to an electrical insulating sintered AlN body having a high thermal conductivity suitable for mounting Si or GaAs semiconductor devices and a process for preparing the same.
(2) Description of the Prior Art
Recently, circuit-constituting devices such as semi-conductor chips, etc. have been mounted on semi-conductor substrates for use in large-scale integrated circuits, etc. with a very high density. On the other hand, needs for large capacity and smaller scale have been more and more increased, and the quality of heat generated per unit area during the working of a semi-conductor device becomes considerably larger. Thus, substrate materials having a better heat radiation, a better electrical insulation and a higher dielectric strength have been in a keen demand. Specifically, materials having a better heat radiation and also a better electrical insulation have been desired for power semi-conductor substrates, power module hybrid substrates, semi-conductor package substrates, semi-conductor laser heat sink, etc.
As electrical insulating substrate materials according to the prior art, mainly sintered alumina body has been used. However, substrates made from the sintered alumina body are not better in the heat radiation, and consequently development of electrical insulating substrate materials having a better heat radiation has been desired. Such electrical insulating substrate materials must meet the following requirements.
(1) higher electrical resistivity, PA1 (2) higher thermal conductivity, PA1 (3) similar coefficient of thermal expansion to that of Si or GaAs single crystal, PA1 (4) lower dielectric constant or dielectric loss, PA1 (5) higher mechanical strength, etc.
To meet the foregoing requirements, a sintered SiC body containing a Be compound is proposed in Japanese patent application Kokai (Laid-open) No. 57-2591 as an electrical insulating substrate material having a good heat radiation. The proposed sintered body has many characteristics of a substrate material having a good radiation such as a high thermal conductivity, a good electrical insulation, the coefficient of thermal expansion being similar to that of Si single crystal, etc. but its current-voltage characteristics show varistor characteristics, and the electrical resistivity decreases with increasing electric field intensity. Furthermore, its dielectric constant is as large as about 40 at 1 MHz. In other words, a sintered body of SiC-Be compound system cannot be used as an electrical insulating substrate material when the electric field intensity is high, and is not preferable as a substrate material for a circuit that transmits a signal at a high speed.
On the other hand, a sintered AlN body has been developed as a substrate material having a good heat radiation. The sintered AlN body is a material having many characteristics such as higher electrical resistivity and insulating strength, lower dielectric constant, etc., but its thermal conductivity is less than 200 W/m..degree.K.
Journal of American Ceramic Society 66 (5) C-40 to C-41 (1983) discloses an influence of a hot press temperature upon the thermal conductivity and thermal diffusivity of sintered bodies of SiC-AlN system, where the thermal conductivity of only less than 100 W/m.degree.K. is obtained.
Japanese patent applications Kokai (Laid-open) Nos. 58-91059 and 59-69474 disclose sintered bodies of SiC-AlN system containing a sintering additive and a process for preparing the same. The disclosed sintered bodies have a good electrical insulation, but the thermal conductivity of the sintered bodies disclosed in said Japanese patent application Kokai (Laid-open) No. 58-91059 is maximum 138 W/m/.degree.K., and that disclosed in said Japanese patent application Kokai (Laid-open) No. 59-69474 is maximum 105 W/m.degree.K.
The sintered SiC bodies, sintered AlN bodies and sintered bodies of SiC-AlN system have several, much distinguished characteristics, but are still not satisfactory in several points. The sintered SiC bodies still have tasks such as an increase in the dielectric strength and a decrease in the dielectric constant. The sintered AlN bodies and sintered bodies of SiC-AlN system still have a task such as an increase in the thermal conductivity.